c-myc and c-ets (1 and 2) genes are cellular homologues of the oncogenes carried by the avain melocytomatosis virus MC29 and the avian acute leukemia virus E26, respectively. These genes are suspected to have some roles in the parogenesis of certain types of human malignancy. Production of monoclonal antibodies against products of these genes was planned for application to the biological and biochemical characterization of these products. A monoclonal antibody reactive with human c-myc proteins has been isolated using a synthetic oligopeptide antigen. This antibody detects an additional polypeptide in addition to c-myc proteins, and its possible relationship to c-myc products is being investigated. In the course of pulse-labeling and subsequent chase of COLO 320 cells, four different polypeptides have been detected by this antibody. They possibly represent different species of human c-myc proteins and precursor-product relationships are suggested between some of these polypeptides. Proteins recognized by this antibody are being purified for amino acid sequencing studies.